Thermal management of integrated emission reduction system

ABSTRACT

The present invention involves thermal management of an integrated emission reduction system for the removal of particulate matter and NOx from diesel engine exhaust streams. The inventive integrated emission reduction system may include a diesel particulate filter (DPF), a heat source for adjusting the temperature of the exhaust stream entering the DPF, at least one catalytic absorber of NOx, a heat exchanger for adjusting the temperature of the exhaust stream entering the NOx absorber, and a computing device to monitor the temperature of the exhaust stream entering the DPF and the NOx absorber, and to control the operation of the heat exchanger and heat source, thereby improving the efficiency of the DPF and the NOx absorber.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to exhaust emission reduction systems for the removal of particulate matter and nitrogen oxides (NOx) from diesel engine exhaust streams, and, more particularly, to improving the efficiency of emission reduction systems having a nonselective catalytic reduction component.

[0003] 2. Description of the Related Art

[0004] Diesel engine combustion exhausts include carbon dioxide, carbon monoxide, unburned hydrocarbons, NOx, and particulate matter (PM). Increasingly, environmental regulations call for emissions controls to progressively lower diesel exhaust emission levels for NOx and PM. For example, EURO 4 (2005) and EURO 5 (2008) and U.S. 2004 and U.S. 2007 emissions limit standards. Regulations are increasingly limiting the amount of NOx that can be emitted during a specified drive cycle, such as an FTP (Federal Test Procedure) in the United States or an MVEG (Mobile Vehicle Emission Group) in Europe.

[0005] One of the ways known in the art to remove NOx from diesel engine exhaust gas is by catalyst reduction. A catalyst reduction method essentially comprises passing the exhaust gas over a catalyst bed in the presence of a reducing gas to convert the oxidized nitrogen to elemental nitrogen. Two types of catalytic reduction are nonselective catalyst reduction (NSCR) and selective catalyst reduction (SCR). This invention relates to emission reduction systems including NSCR.

[0006] Roth et al., U.S. Pat. No. 6,446,430, discloses a method and apparatus for reducing transient and steady-state NOx emissions in the exhaust gases of a vehicle powered by a diesel-fueled internal combustion engine which includes a reducing catalytic converter downstream of the engine. The catalytic converter includes a reducing catalyst and a system for injecting fuel oil as hydrocarbon (HC) reductant into the exhaust gas upstream of the catalytic converter. Roth recognizes that transient engine conditions will increase the temperature of the exhaust gas which, in turn, will raise the temperature of the catalytic converter to the point where the temperature window in which NOx conversion occurs may be exceeded.

[0007] Conversion efficiency of some NOx catalysts is temperature dependent. The efficient operation temperature range is generally between 250° and 450° C. (degrees Celsius), depending on the catalyst, and above 750° to 800° C. the catalyst may be damaged. During diesel engine operations involving high loads, exhaust gas temperatures can easily exceed these ranges.

[0008] Diesel particulate filters (DPF) for the removal of PM from a diesel engine exhaust stream have been proven to be extremely efficient at removing carbon soot. The most widely used diesel trap is the wall flow filter which filters the diesel exhaust by capturing the PM on the porous walls of the filter body. Cutler et al., U.S. Pat. No. 6,464,744, discloses a porous ceramic diesel exhaust particulate filter. The ceramic filter includes a plurality of end-plugged honeycomb structures which in combination act to trap and combust diesel exhaust particulates. As PM collects, eventually the pressure drop across the filter rises to create back pressure against the engine and regeneration of the filter becomes necessary. The regeneration process involves heating the filter to initiate combustion of the carbon soot. Normally, the regeneration is accomplished under controlled conditions of engine management whereby a slow burn is initiated and lasts a number of minutes, during which the temperature in the filter rises from about 400° to 600° C. to a maximum of about 800° to 1,000° C.

[0009] In currently available systems, there is a problem of effective combustion of diesel PM at exhaust streams temperatures of 300° C. or below. While the temperature of diesel exhaust stream may exceed 500° C., it may be lower, e.g., 300° C. or below, and, as noted above, filters are not particularly effective for combusting trapped PM at such low temperatures.

[0010] As noted above, DPF regeneration normally requires exhaust gas temperatures of at least 600° C., though some filters continuously regenerate by including catalytic additives that provide soot ignition temperatures between 350° and 450° C. However, diesel engines operating under a low load condition may produce exhaust gas having a temperature too low to burn PM in even catalytic DPFs.

[0011] While the above systems have been found beneficial in reducing certain diesel exhaust emissions, it has also been found beneficial if such systems are operated at temperatures that maximize their efficiency. Specifically, DPFs operate most efficiently at a temperature above a particular threshold, often a temperature higher than typical diesel exhaust stream temperatures, and NOx catalysts operate most efficiently in a temperature window that is often below typical exhaust stream temperatures.

SUMMARY OF THE INVENTION

[0012] The present invention involves thermal management of an integrated emission reduction system for the removal of particulate matter (PM) and nitrogen oxides (NOx) from diesel engine exhaust streams. The inventive integrated emission reduction system may include a diesel particulate filter (DPF), a heat source for adjusting the temperature of the exhaust stream entering the DPF, at least one catalytic absorber of NOx, a heat exchanger for adjusting the temperature of the exhaust stream entering the NOx absorber, and a computing device for monitoring the temperature of the exhaust stream entering the DPF and the NOx absorber, and for controlling the operation of the heat exchanger and heat source, thereby improving the efficiency of the DPF regeneration and the NOx absorber.

[0013] An exemplary embodiment of the emission reduction system receives an exhaust stream from a diesel engine powering a vehicle. The exhaust stream is directed through a DPF, a heat exchange system, an NOx absorber system, a diesel oxidation catalyst (DOC), and a muffler. The emission reduction system includes an electronic control unit (ECU) for monitoring and controlling the exhaust stream emission reduction process.

[0014] Conversion efficiency of NOx catalysts is temperature dependent and incineration of PM is also temperature dependent. Therefore, it is beneficial if the exhaust stream entering various emission reduction system components, such as the DPF and the NOx absorber, are adjusted to a temperature that maximizes the efficiency of the system components. Specifically, it is often beneficial to increase the temperature of the exhaust stream entering the DPF, and to increase or decrease the temperature of the exhaust stream entering the NOx absorber to a specific temperature window.

[0015] In one form, an exhaust emission reduction system for reducing exhaust stream emissions produced by a diesel engine includes a particulate filter contained within the exhaust stream, a heat exchanger to adjust the temperature of the diesel exhaust stream, at least one catalytic absorber of NOx within the temperature-adjusted diesel exhaust stream, and a heat source capable of heating the exhaust stream.

[0016] In another form thereof, a method of controlling an exhaust emission reduction system for reducing exhaust stream emissions produced by a diesel engine includes the steps of monitoring and controlling the temperature of the exhaust stream entering a particulate filter, thereby improving the operation of the particulate filter, and monitoring and controlling the temperature of the exhaust stream entering a catalytic absorber of NOx, thereby improving the operation of the NOx absorber.

[0017] In yet another form thereof, a computer device for controlling an exhaust emission reduction system for reducing exhaust stream emissions produced by a diesel engine; the emission reduction system including a particulate filter, catalytic absorber of NOx system, and a thermal transfer system capable of adding heat to or removing heat from the exhaust stream; the computing device includes a microprocessor (“processor”) and software capable of monitoring the temperature of the exhaust stream entering the particulate filter, controlling the thermal transfer system to adjust the temperature of the exhaust stream for improving operation of the particulate filter, monitoring the temperature of the exhaust stream entering the absorber, and controlling the thermal transfer system to adjust the temperature of the exhaust stream for improving operation of the absorber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0019]FIG. 1 is an assembly view of an integrated emission reduction system provided on a diesel engine-powered vehicle according to the present invention;

[0020]FIG. 2 is a plan form view of the integrated emission reduction system of FIG. 1;

[0021]FIG. 3 is a block diagram of a control system for controlling the integrated emission reduction system of FIG. 1;

[0022]FIG. 4 is a process diagram of the integrated emission reduction system of FIG. 1; and

[0023] FIGS. 5A-5D are software flow diagrams of the control device of FIG. 3.

[0024] Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present invention. The exemplification set out herein illustrates embodiments of the invention, in several forms, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DESCRIPTION OF THE PRESENT INVENTION

[0025] The embodiments disclosed below are not intended to be exhaustive or limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings.

[0026] Vehicle 12, shown in FIG. 1, is powered by a diesel engine and includes integrated emission reduction system 10 for removing particulate matter (PM) and nitrogen oxides (NOx) from diesel engine exhaust stream 17, shown in FIG. 2. Referring to FIGS. 1 and 2, emission reduction system 10 generally includes diesel particulate filter (DPF) 20, heat source 30, heat exchange system 40, NOx absorber system 60, diesel oxidation catalyst (DOC) 80, muffler 90, exhaust pipe 96, and control system 100, shown in FIG. 3. The inventive method and control system 100 for thermal management of inventive integrated emission reduction system 10 provides increased efficiency for emission reduction systems having a nonselective catalytic reduction (NSCR) component, such as NOx absorber system 60.

[0027] Referring to FIG. 2, DPF 20 includes filter structure 22 for trapping and combusting diesel exhaust PM, such as carbon soot. Filter structure 22 is well known in the art and may be, for example, a porous ceramic forming a plurality of end-plugged honeycomb structures that are efficient at removing carbon soot from the exhaust of diesel engines. In a continuously regenerating catalytic DPF, filter structure 22 includes a catalyst. DPF 20, in the exemplary embodiment, may include, for example, a filter manufactured by Corning Incorporated of Corning, N.Y., such as the one that is the subject of U.S. Pat. No. 6,464,744.

[0028] Heat source 30 is capable of increasing the temperature of the exhaust of diesel engines. Specifically, heat source 30 should be capable of increasing the exhaust temperature to the ignition temperature of carbon soot, which may be in the range of at least 600° to 650° C., or at least 300° to 350° C. if a catalytic treated DPF is used. Set point S1, hereinafter defined as a temperature sufficient to combust carbon soot, is in the range of 600° to 650° C. Heat source 30 in the exemplary embodiment, for example, includes a diesel fuel-fired burner, such as is available from ArvinMeritor of Columbus, Ind. Such a heat source 30 includes fuel control 32 for controlling diesel fuel supplied to heat source 30, fuel atomizer air control 34 for controlling the atomization of the diesel fuel for combustion, and air blower control 36 for controlling air flow for the combustion of the diesel fuel by heat source 30.

[0029] Heat exchange system 40 provides temperature adjustment, generally cooling, of diesel engine exhaust. Heat exchange system 40 includes exchange path 42 and bypass path 44 coupled as parallel conduits for a flow of diesel engine exhaust. Exchange path 42 contains heat exchanger 50, which includes heat exchange structure 56 supplied with a flow of coolant controlled by coolant control valve 51 and provided via coolant inlet 52 and coolant outlet 54. The coolant may be from an existing engine cooling system, provided additional cooling capacity is available, for example, for a light-duty vehicle, or from a separate independent cooling system, for example, for a heavy-duty vehicle in which reserve cooling capacity may be limited.

[0030] Bypass path 44 includes heat exchange bypass valve 46, which, in the exemplary embodiment, may be a high-temperature exhaust gas control valve, such as Part No. 2010499, manufactured by ArvinMeritor of Columbus, Ind. Flow of the engine exhaust through heat exchanger 50 is dependent on the resistance to flow provided in bypass path 44 by valve 46. For example, if valve 46 closes bypass path 44, the flow of engine exhaust through heat exchanger 50 will be increased, and, if valve 46 is open allowing flow of exhaust through bypass path 44, the flow of engine exhaust through heat exchanger 50 will be decreased. An exemplary heat exchanger 50 is Part No. 1202496, manufactured by Behr America, Inc. of Troy, Mich.

[0031] NOx absorber system 60 includes at least one catalyst absorber for NOx 62 a. NOx absorber 62 a provides nonselective catalyst reduction (NSCR) that converts engine exhaust NOx into nitrogen. NOx absorber 62 a may include catalyst 64 a, such as, for example, potassium or barium based catalyst supported by a ceramic or metallic substrate. To recharge NOx absorber 62 a when it has reached capacity, hydrocarbons (HC) in the form of diesel fuel injected into NOx absorber 62 a by reductant injector system 70 a may be used to desorb and regenerate catalyst 64 a. NOx absorber system 60 may include additional NOx absorbers that are operable in series or in parallel to absorber 62 a.

[0032] NOx absorber system 60 in the exemplary embodiment, shown in FIG. 2, includes a first and second NOx absorber 62 a and 62 b through which engine exhaust is selectively delivered by control of first and second absorber control valve 68 a and 68 b. First absorber valve 68 a controls the flow of engine exhaust through first absorber input path 66 a, which is coupled to first NOx absorber 62 a. Second absorber valve 68 b controls the flow of engine exhaust in second absorber input path 66 b, which is coupled to second NOx absorber 62 b. First and second outlet paths 76 a and 76 b, each coupled to first and second NOx absorber 62 a and 62 b, respectively, connect together to complete the parallel flow circuit of NOx absorber system 60.

[0033] First and second injector systems 70 a and 70 b used in the exemplary embodiment may be of the type available from ArvinMeritor. Exemplary first and second NOx absorbers 62 a and 62 b may be, for example, NOx absorbers manufactured by Engelhard Corporation of Iselin, N.J., and Johnson Matthey of London, England. First and second absorber valves 68 a and 68 b in the exemplary embodiment may be, for example, high-temperature exhaust gas control valves manufactured by ArvinMeritor.

[0034] Diesel oxidation catalyst (DOC) 80 reduces the unburned HC and carbon monoxide (CO) present in diesel exhaust. DOC 80 catalyses the oxidation of the unburned HC and CO. Such devices are well known in the art. A suitable example is available from ArvinMeritor.

[0035] Muffler 90 and exhaust pipe 96 provide engine exhaust noise reduction and directing of vented engine exhaust stream 98.

[0036] Referring to FIG. 3, control system 100 for thermal management and regeneration of integrated emission reduction system 10 includes control device 101. Control device 101 is a processor based control system containing a processor which may include, for example, RAM (random access memory), FLASH animation technology, EEPROM (electrically erasable programmable read-only memory), on-board CAN (controller area network), etc., and software capable of executing process control, shown in FIGS. 5A-5D, for monitoring and controlling various aspects of emission reduction system 10. Such an exemplary control device 101 may be implemented as part of an engine control unit (ECU).

[0037] In the present invention, control device 101 receives input signal information from engine RPM 15, turbocharger RPM 16, DPF inlet pressure sensor 24, DPF inlet temperature sensor 25, DPF outlet pressure sensor 26, DPF outlet temperature sensor 27, air blower control 36, NOx inlet temperature sensor 56, NOx inlet sensor 72, and NOx outlet sensor 74. Upon receiving any of the aforementioned input signal information, control device 101 processes the received data and generates output signals to control fuel control 32, fuel atomizer 34, air blower control 36, heat exchanger valve 46, coolant valve 51, NOx adsorber A valve 68 a, NOx adsorber B valve 68 b, reductant injector A 70 a, and reductant injector B 70 b.

[0038] Referring generally to FIGS. 2 and 4, in the exemplary embodiment, engine exhaust stream 17 from the diesel engine is delivered to integrated emission reduction system 10 via engine exhaust connection 18. Engine exhaust connection 18 is coupled to DPF 20. The temperature T1 and pressure P1 of exhaust stream 17 entering DPF 20 are monitored by control device 101 using DPF inlet pressure sensor 24 and DPF inlet temperature sensor 25. Control device 101 may control the temperature of exhaust stream 17 entering DPF 20 by controlling heat source 30. Specifically, control device 101 may control fuel control 32, fuel atomizer air control 34, and combustion air blower control 36, to increase the temperature T1 of exhaust stream 17 entering DPF 20 to an optimum temperature range for operation of the DPF.

[0039] The temperature T2 and pressure P2 of exhaust stream 17 exiting DPF 20 is monitored by control device 101 using DPF outlet pressure sensor 26 and DPF outlet temperature sensor 27.

[0040] The flow of exhaust stream 17 through heat exchange system 40 and the resulting temperature change to exhaust stream 17 is controlled by control device 101 using heat exchanger valve 46 and coolant valve 51. Additionally, the cooling of exhaust stream 17 passing through heat exchange system 40 is controlled by the flow of exhaust stream 17 through heat exchanger 50, a function of heat exchanger bypass valve 46 partially or fully opening or closing bypass path 44 and forcing exhaust stream 17 through heat exchanger 50, and also a function of the flow of coolant through heat exchanger 50 controlled by coolant valve 51.

[0041] The temperature T3 of exhaust stream 17 exiting heat exchange system 40 and entering NOx absorber system 60 is monitored by control device 101 using NOx inlet temperature sensor 56. As necessary, the temperature of the exhaust stream is lowered by heat exchange system 40 from the temperature of the exhaust stream of the particulate filter in the direction of an optimized temperature for NOx absorption.

[0042] First and second absorber valves 68 a and 68 b control the flow of exhaust stream 17 through NOx absorber system 60 so that one of first and second NOx absorbers 62 a and 62 b is in operation and receives exhaust stream 17 flow, while the other of first and second NOx absorber 62 a and 62 b is in regeneration and is supplied reductant by first or second reductant injector systems 70 a or 70 b to restore the capacity of catalyst 64 a or 64 b.

[0043] In order for control device 101 to monitor the efficiency and remaining capacity of first and second NOx absorbers 62 a and 62 b, NOx absorber system 60 may include NOx inlet sensor 72 for monitoring NOx content N1 at an inlet to NOx absorber system 60 and NOx outlet sensor 74 for monitoring NOx content N2 at an outlet of NOx absorber system 60. Control device 101 may then monitor NOx content of exhaust stream 17 entering and exiting NOx absorber system 60 and determine when currently operating NOx absorber 62 a or 62 b requires regeneration. However, NOx sensors are currently cost-prohibitive for most commercially practical diesel engine-powered vehicle applications; therefore, control device 101 may provide switching between NOx absorbers 62 a and 62 b based on other engine operations parameters and predicted NOx levels, elapsed time of engine operation, or some combination of these and other factors.

[0044] Exhaust stream 17 exiting NOx absorber system 60 is supplied to DOC 80 for removal of unburned HC and CO. Finally, exhaust stream 17 flows through sound-reducing muffler 90 and exhaust pipe 96, exiting integrated emission reduction system 10 as vented exhaust stream 98.

[0045] Thermal management of integrated emission reduction system 10 provides improved efficiency of the removal of NOx and PM from diesel engine exhaust stream 17. In particular, a thermal transfer system, including heat source 30 and heat exchange system 40 in the exemplary embodiment, is controlled by control device 101 to adjust the temperature of exhaust stream 17 entering DPF 20 and to adjust the temperature of exhaust stream 17 entering NOx absorber system 60 to a temperature window, thereby increasing the efficiency of the operation of DPF 20 and NOx absorber system 60.

[0046] DPF 20 provides trapping and incineration of PM, generally carbon soot. At low engine load conditions, exhaust stream 17 may have a temperature of 300° C. or below. Generally, available DPFs are not particularly effective for combusting PM at such low temperatures. Monitoring of DPF inlet temperature T1 by sensor 25 allows control device 101 to increase the temperature of exhaust stream 17 entering DPF 20 by controlling heat source 30. Heat source 30 is capable of increasing exhaust stream 17 temperatures to a range providing more effective regeneration of a continuously regenerating catalytic DPF 20. For example, increasing exhaust stream 17 temperature entering DPF 20 to above 270° C., preferably more than 300° C., more preferably more than 350° C. Set point S2, hereinafter defined as an efficient minimum operating temperature for DPF 20, is in the range of 300° to 350° C.

[0047] Additionally, heat source 30 may be capable of providing regeneration of a non-continuous regenerating non-catalytic DPF 20. Control device 101 monitors DPF inlet pressure P1 and DPF outlet pressure P2 using inlet pressure sensor 24 and outlet pressure sensor 26 to determine whether excess trapped particulate matter in DPF 20 requires that DPF 20 be recharged. Excess trapped PM in DPF 20 may result in excessive back pressure in exhaust stream 17 and against the diesel engine. Excess trapped PM is removed from DPF 20 by a regeneration cycle consisting of increasing the temperature within DPF 20 so that trapped PM is incinerated. This may be accomplished, for example, by periodic increase in the temperature of exhaust stream 17 using heat source 30 to a temperature more than 600° C., and preferably more than 650° C., but less than a temperature causing damage to filter structure 22 within DPF 20, for example, less than 1000° C., and more preferably less than 900° C.

[0048] NOx absorber system 60 provides increased efficiency when the temperature T3 of exhaust stream 17 entering first or second NOx absorbers 62 a or 62 b is within a temperature window that provides increased efficiency for the specific absorber coating 64 a and 64 b that is used. For example, for a potassium based absorber, the temperature of exhaust stream 17 entering first and second NOx absorbers 62 a and 62 b may be more than 250° C., preferably more than 300° C., and more preferably more than 360° C., but less than 450° C., preferably less than 435° C., more preferably less than 420° C. Set point S3, hereinafter defined as an efficient operating temperature window for NOx absorbers 62 a and 62 b, is in the range of 360° to 420° C.

[0049] If another absorber coating 64 a and 64 b is provided, for example barium, a slightly different temperature window is preferred according to the operating efficiency of the catalyst. Thus, for low engine load conditions or immediately after startup, exhaust stream 17 may have a temperature below the preferred temperature window, and thus control device 101 may control heat source 30 to increase NOx absorber inlet temperature T3 to within the preferred temperature window.

[0050] Additionally, during normal engine load conditions, or because of increased heating of exhaust stream 17 by heat source 30 for increased efficiency of DPF 20, it is likely that the temperature T3 of exhaust stream 17 entering NOx absorber system 60 will be higher than the preferred temperature window. Therefore, control device 101 may control cooling of exhaust stream 17 by partially or fully closing exhaust stream 17 flow through bypass path 44 using valve 46, and increased coolant flow by partially or fully opening coolant control valve 56, which provides coolant to heat exchanger 50, and thus reduces temperature T3 of exhaust stream 17 entering NOx absorber system 60.

[0051] First and second NOx absorbers 62 a and 62 b may develop reduced capacity because of absorbed substances (attributable to diesel fuel sulfur content) providing competition with NOx for absorber coating 64 a and 64 b storage sites. Restoring the capacity of first and second NOx absorbers 62 a and 62 b is possible by increasing the temperature of exhaust stream 17 provided through first and second NOx absorbers 62 a and 62 b sufficiently to free the absorbed substances attributed to diesel fuel sulfur content. For example, periodic regeneration may include control device 101 controlling heat source 30 to increase the temperature T3 of exhaust stream 17 entering first and second NOx absorbers 62 a and 62 b to more than 500° C., preferably more than 550° C., more preferably more than 600° C. Set point S4, hereinafter defined as a temperature sufficient to free absorbed substances from absorber coating 64 a and 64 b storage sites, is in the range of 550° C. to 600° C.

[0052] Control device 101 is also capable of selectively directing exhaust stream 17 to one of first NOx absorber 62 a and second NOx absorber 62 b. For example, control device 101 may close second absorber valve 68 b blocking exhaust stream 17 from entering second absorber input path 66 b, and open first absorber valve 68 a providing exhaust stream 17 flow through first absorber input path 66 a. Thus, first NOx absorber 62 a is in operation for absorbing NOx from exhaust stream 17, and NOx absorber 62 b may be simultaneously regenerated.

[0053] Regeneration may include second injection system 70 b providing HC in the form of diesel fuel which acts as a reductant to desorb and regenerate the NOx catalyst 74 b. Upon regeneration of NOx absorber 62 b, control device 101 may close first absorber valve 68 a and open second absorber valve 68 b, thus placing into operation NOx absorber 62 b and similarly providing for simultaneous regeneration of first NOx absorber 62 a, which may include first injection system 70 a providing HC in the form of diesel fuel.

[0054] Switching between first and second NOx absorbers 62 a and 62 b for operation and regeneration may be determined by control device 101 based on predicted NOx output and capacity of first and second NOx absorbers 62 a and 62 b for given engine operating parameters, elapsed engine time and elapsed time since last regeneration, a combination of these parameters, or measurement of actual NOx content N1 at the NOx absorber system 60 inlet and actual NOx content N2 at NOx absorber system 60 outlet. Although the exemplary embodiment may include NOx inlet sensor 72 and NOx outlet sensor 74 for monitoring actual NOx content N1 and N2 of exhaust stream 17, predicted or actual diesel engine operating parameters, including engine RPM 15 and turbocharger RPM 16 and other parameters related to NOx content of exhaust stream 17, may also or may alternatively be used to selectively regenerate first and second NOx absorbers 62 a and 62 b.

[0055] Referring now to FIGS. 5A-5D, control device 101 contains a processor and software operably associated with the processor and adapted to carry out modules for controlling emission reduction system 10. For the purposes of this invention, a module is a part of the software that contains one or more functions. Each function performs a specific task. Each module includes multiple conditional statements, i.e., statements that enable the modules to act differently each time that they are executed depending on an input value provided by the processor. FIGS. 5A-5D exhibit the process control flow when the software is executed by control device 101.

[0056] Referring to FIG. 5A, when control device 101 executes the software, module A 102 is executed. Module A 102 provides thermal management process control for regeneration of DPF 20 and for temperature control of exhaust stream 17 entering NOx absorber system 60. Upon execution of module A 102, conditional statement 104 (i.e., whether DPF regeneration is needed) must be satisfied. If the processor returns input value TRUE, then module A 102 performs function 110 to operate heat source 30 and control the temperature measured at DPF inlet temperature T1 to set point S1. After performing function 110, module A 102 must satisfy conditional statement 112 (i.e., whether NOx absorber inlet temperature T3 is at set point S3). If the processor returns input value FALSE, then module A 102 performs function 114 to adjust heat exchanger 40 coolant flow valve 51 and bypass valve 46. After performing function 114, module A 102 again must satisfy conditional statement 112 (i.e., whether NOx absorber inlet temperature T3 is at set point S3). As long as the processor returns input value FALSE from conditional statement 112, conditional statement 112 and function 114 are repeatedly satisfied and performed, respectively, until NOx absorber inlet temperature T3 reaches set point S3 and the processor returns input value TRUE to conditional statement 112. If conditional statement 112 returns input value TRUE, then conditional statement 116 (i.e., whether DPF regeneration is complete) must be satisfied by module A 102. If the processor returns input value FALSE, then conditional statements 112 and 116 must be respectively satisfied until the processor returns input value TRUE to both. If the processor returns input value TRUE to conditional statement 116, then module A 102 performs function 118 to turn off heat source 30. After function 118 is performed, module A 102 is re-executed beginning at conditional statement 104.

[0057] If the processor returns input value FALSE to conditional statement 104 (i.e., whether DPF regeneration is needed), then conditional statement 130 (i.e., whether NOx inlet temperature T3 is at set point S3) must be satisfied. If the processor returns input value TRUE, then module A 102 is re-executed beginning at conditional statement 104. If the processor returns input value FALSE, then module B 103 is executed and conditional statement 132 (i.e., whether NOx inlet temperature T3 is too high) must be satisfied. If the processor returns input value TRUE, then conditional statement 134 (i.e., whether heat source 30 is on) must be satisfied by module B 103. If the processor returns input value TRUE, then module B 103 performs function 136 to either reduce fuel flow or turn off heat source 30. After function 136 is performed by module B 103, conditional statement 132 must again be satisfied. If the processor returns input value FALSE to conditional statement 134, then module B 103 performs function 138 to adjust heat exchanger 50 coolant flow valve 51 and bypass valve 46. After performing function 138, module B 103 must satisfy conditional statement 140 (i.e., whether heat exchanger 50 has coolant flow). If the processor returns input value FALSE, then module B 103 performs function 142 to set off an alarm. The alarm alerts control device 101, which then produces notification and/or corrective action, for example, reducing engine load conditions and enabling an engine check light. If the processor returns input value TRUE to conditional statement 140, module B 103 is re-executed and conditional statement 132 must be satisfied.

[0058] If the processor returns input value FALSE to conditional statement 132, module B 103 must satisfy conditional statement 150 (i.e., whether NOx inlet temperature T3 is too low). If the processor returns input value FALSE, then process control returns to module A 102 to be re-executed beginning at conditional statement 104. If the processor returns input value TRUE to conditional statement 150, then conditional statement 152 (i.e., whether coolant is flowing in heat exchanger 50) must be satisfied. If the processor returns input value TRUE to conditional statement 152, then module B 103 performs function 154 to reduce coolant flow and/or bypass flow. After module B 103 performs function 154, module B 103 is re-executed beginning at conditional statement 132. If the processor returns input value FALSE to conditional statement 152, module B 103 performs function 156 to either turn on heat source 30 or increase the fuel flow. After function 156 is performed, module B 103 is re-executed beginning at conditional statement 132. Module B 103 is executed until process control returns to module A 102 when the processor returns input value FALSE to conditional statement 150. Module A 102 is executed until diesel engine exhaust stream 17 ceases.

[0059] Referring now to FIG. 5B, when control device 101 executes the software, module C 200 may also be executed. Module C 200 may be simultaneously or selectively executed with other software modules, or may be integrated into module A 102. Module C 200 provides thermal management process control of a minimum temperature for exhaust stream 17 entering DPF 20. Upon execution of module C 200, conditional statement 202, whether DPF 20 inlet temperature T1 is at minimum temperature set point S2, must be satisfied. If the processor returns input value FALSE, then module C 200 performs function 204 to operate heat source 30 and control the temperature measured at DPF inlet temperature T1 to set point S2. After function 204 is performed, module C 200 is re-executed beginning at conditional statement 202. If the processor returns input value TRUE at condition statement 202, module C 200 returns to conditional statement 202. Module C 200 may be executed until diesel engine exhaust stream 17 ceases.

[0060] Referring to FIG. 5B, when control device 101 executes the software, module D 300 is executed. Module D 300 provides thermal management process control of desulfurization of NOx absorber system 60. Module D 300 may be simultaneously or selectively executed with other software modules, or may be integrated into module A 102. If conditional statement 302, whether NOx absorber system 60 desulfurization is needed, returns input value TRUE, then module D 300 performs function 304 to operate heat source 30 and control the temperature measured at NOx absorber inlet T3 set point S4. After performing function 304, module D 300 must satisfy conditional statement 306 (i.e., whether NOx inlet temperature T3 is at set point S4). If the processor returns input value FALSE, then module D 300 performs function 308 to adjust heat source 30 fuel flow. After performing function 308, module D 300 again must satisfy conditional statement 306. As long as the processor returns input value FALSE from conditional statement 306, conditional statement 306 and function 308 are repeatedly satisfied and performed respectively, until NOx absorber inlet temperature T3 reaches set point S4 and the processor returns input value TRUE to conditional statement 306. If conditional statement 306 returns input value TRUE, then conditional statement 310 (i.e., whether NOx desulfurization is complete) must be satisfied by module D 300. If the processor returns input value FALSE, then conditional statements 306 and 310 must be respectively satisfied until the processor returns input value TRUE to both. If the processor returns input value TRUE to conditional statement 310, then module D 300 is re-executed beginning at conditional statement 302. Module D 300 may be executed until diesel engine exhaust stream 17 ceases.

[0061] Referring now to FIG. 5D, when control device 101 executes the software, module E 400 may be executed. Module E 400 provides process control for selectively regenerating NOx absorbers 62 a and 62 b. Software module E 400 may be simultaneously or selectively executed with other software modules, or may be integrated into software module A 102. Module E 400 performs function 402 to open NOx absorber A valve 68 a and function 404 to close NOx absorber B valve 608 b. After performing function 404, conditional statement 406 (i.e., whether NOx absorber A 62 a requires regeneration) must then be satisfied. If the processor returns input value TRUE, then module E 400 sequentially performs function 408 to open NOx absorber B valve 68 b, function 110 to close NOx absorber A valve 68 a, and function 412 to activate reductant injector A 70A/absorber A 62 a regeneration. If the processor returns input value FALSE for conditional statement 406, then module E 400 returns to conditional statement 406 repeatedly until the processor returns input value TRUE. After executing function 412, conditional statement 414 (i.e., whether NOx absorber A 62 a regeneration is complete) must be satisfied. If the processor returns input value FALSE, then module E 400 repeatedly performs function 412 and must satisfy conditional statement 414 until regeneration is complete and the processor returns input value TRUE to conditional statement 414. If conditional statement 414 returns input value TRUE, then conditional statement 416 (i.e., whether NOx absorber B 62 b needs regeneration) must be satisfied by module E 400. If conditional statement 416 returns input value FALSE, then conditional statement 416 is repeatedly executed until the processor returns input value TRUE. If the processor returns input value TRUE to conditional statement 416, then module E 400 sequentially performs function 418 to open NOx absorber A valve 68 a, function 420 to close NOx absorber B valve 68 b, and function 422 to activate reductant injector B 70 b/absorber B 62 b regeneration. After module E 400 performs function 422, conditional statement 424 (i.e., whether regeneration of NOx absorber B 62 b is complete) must be satisfied. If the processor returns input value FALSE, then module E 400 repeatedly performs function 422 and must satisfy conditional statement 424 until NOx absorber 62 b regeneration is complete. If the processor returns input value TRUE for conditional statement 424, then module E 400 is re-executed beginning at conditional statement 406.

[0062] While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains. 

What is claimed is:
 1. An exhaust emission reduction system for reducing exhaust stream emissions produced by a diesel engine, comprising: a particulate filter contained within the exhaust stream; a heat exchanger to adjust the temperature of the diesel exhaust stream; and at least one catalytic absorber of NOx within the temperature adjusted diesel exhaust stream.
 2. The emission reduction system of claim 1, wherein the diesel engine is adapted for powering a vehicle.
 3. The emission reduction system of claim 1, further comprising a diesel oxidation catalyst within the exhaust stream.
 4. The emission reduction system of claim 1, wherein said at least one NOx absorber includes at least two NOx absorbers coupled in parallel; and the emission reduction system further comprises at least one valve capable of selectively directing the exhaust stream to said NOx absorbers.
 5. The emission reduction system of claim 4, wherein said NOx absorbers may be selectively regenerated.
 6. The emission reduction system of claim 4, further comprising a diesel fuel reductant injection system associated with said NOx absorbers, said reductant injection system capable of delivering reductant to said NOx absorbers for regeneration.
 7. The emission reduction system of claim 1, where said at least one NOx absorber includes at least two NOx absorbers coupled in parallel; and the emission reduction system further comprises at least one valve adapted for selectively isolating said NOx absorbers from the exhaust stream.
 8. The emission reduction system of claim 1, wherein the exhaust stream is cooled to a temperature for improved operation of said at least one NOx absorber.
 9. The emission reduction system of claim 8, wherein said temperature is from 250° to 450° C.
 10. The emission reduction system of claim 1, further comprising a heat source capable of heating the exhaust stream.
 11. The emission reduction system of claim 10, wherein said heat source includes a diesel fuel fired burner.
 12. The emission reduction system of claim 10, wherein said heat source is capable of heating the exhaust stream to a temperature for improved operation of said particulate filter.
 13. The emission reduction system of claim 12, wherein said temperature is at least 270° C.
 14. The emission reduction system of claim 12, wherein said heat source is capable of heating the exhaust stream to a temperature sufficient for incineration of a substantial portion of particulates trapped by said filter.
 15. The emission reduction system of claim 10, wherein said heat source is capable of heating the exhaust stream to temperature for improved operation of said NOx absorbers.
 16. The emission reduction system of claim 15, wherein said optimal temperature is from 250° to 450° C.
 17. The emission reduction system of claim 10, wherein said heat source is capable of periodically heating the exhaust stream sufficient to improve the capacity of said NOx absorbers, thereby releasing from said NOx absorbed substances attributable to diesel fuel sulfur content.
 18. The emission reduction system of claim 10, further comprising a computing device capable of monitoring exhaust stream temperatures at the input of said filter and at the input of said first absorber.
 19. The emission reduction system of claim 18, wherein said computing device is further capable of controlling said heat source to adjust said exhaust stream temperature at the input of said filter.
 20. The emission reduction system of claim 18, wherein said computing device is further capable of controlling said heat source to adjust said exhaust stream temperature at the input of said at least one NOx absorber.
 21. The emission reduction system of claim 18, wherein said computing device is further capable of controlling said heater exchanger to adjust said exhaust stream temperature at the input of said at least one NOx absorber.
 22. The emission reduction system of claim 1, wherein said heat exchanger further includes a bypass path having a valve for selectively controlling the flow of the exhaust stream through said bypass path.
 23. A method of controlling an exhaust emission reduction system for reducing exhaust stream emissions produced by a diesel engine, comprising the steps of: (a) monitoring and controlling the temperature of the exhaust stream entering a particulate filter, thereby improving the operation of said particulate filter; and (b) monitoring and controlling the temperature of the exhaust stream entering a catalytic absorber of NOx, thereby improving the operation of said NOx absorber.
 24. The method of claim 21, further comprising the step of: (c) periodically adjusting the temperature of the exhaust stream entering said particulate filter sufficient to incinerate a substantial portion of particulates trapped by said particulate filter.
 25. The method of claim 24, wherein the emission temperature of step (c) is at least 350° C.
 26. The method of claim 24, wherein step (c) is completed when the differential pressure across said particulate filter is above a predetermined level.
 27. The method of claim 23, further comprising the step of: (d) periodically adjusting the temperature of the exhaust stream entering said absorber sufficient to improve the capacity of said NOx absorber, thereby releasing from said NOx absorber absorbed substances attributed to diesel fuel sulfur content.
 28. The method of claim 27, wherein the emission temperature of step (d) is at least 500° C.
 29. The method of claim 23, wherein the exhaust stream temperature of step (a) is at least 270° C.
 30. The method of claim 23, wherein the exhaust stream temperature of step (b) is between 250° and 450° C.
 31. The method of claims 23, 24, or 27, wherein the diesel engine is adapted for powering a vehicle.
 32. A computing device for controlling an exhaust emission reduction system for reducing exhaust steam emissions produced by a diesel engine, the emission reduction system including a particulate filter, a catalytic absorber of NOx, and a thermal transfer system capable of adding heat to or removing heat from the exhaust stream, the computing device comprising a processor and software capable of: monitoring the temperature of the exhaust stream entering the particulate filter; controlling the thermal transfer system to adjust the temperature of the exhaust stream for improved operation of the particulate filter; monitoring the temperature of the exhaust stream entering the absorber; and controlling the thermal transfer system to adjust the temperature of the exhaust stream for improved operation of the absorber.
 33. The computing device of claim 32, wherein the thermal transfer system includes a heat source and a heat exchanger, and said processor and said software are further capable of controlling said heat source and said heat exchanger to adjust the temperature of the exhaust stream entering the particulate filter and the NOx absorber.
 34. The computing device of claim 32, wherein said processor and said software are further capable of: monitoring the pressure differential across the particulate filter; and controlling the thermal transfer system to periodically incinerate particulates trapped by the particulate filter.
 35. The computing device of claim 32, wherein said processor and said software are further capable of controlling the thermal transfer system to periodically adjust the temperature of the exhaust stream to improve the capacity of said NOx absorbers, thereby releasing from said NOx absorbers absorbed substances attributed to diesel fuel sulfur content.
 36. The computing device of claims 33, 34, or 35, wherein the diesel engine is adapted for powering a vehicle and said processor and said software are further capable of receiving engine operating parameters. 